Method of manufacturing electronic parts

ABSTRACT

The method of manufacturing electronic parts comprises the steps of preparing a mother board; mounting element parts on the mother board; providing a thermosetting resin on a surface of the mother board surface on which the element parts are mounted; semi-curing the thermosetting resin so as to be in a range of a stage B condition of the thermosetting resin; splitting the mother board with the thermosetting resin into individual electronic parts each having a divided mother board, at least one element part and the thermosetting resin thereon; and heating the individual electronic parts so that the thermosetting resin in the stage B condition melts first and is then cured permanently.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an electronic part in which oneor more semiconductor elements or the like are mounted on a substrateand sealed with the resin, and a method for manufacturing the same.

[0003] 2. Description of the Related Art

[0004] A conventional electronic part and the method for manufacturingit will be explained with reference to FIGS. 9-13. In most commercialprocesses, a large number of electronic components are mounted on arelatively large mother board which is then cut into smaller pieces eachdefining a respective electronic component. A simple example of thisprocess, but with only four electronic components being mounted on themother board, will be described below.

[0005] As indicated in a perspective view of FIG. 9, a printed circuitboard 111 in which through holes 112 are formed at the prescribedpositions is prepared. Wiring patterns 113 are formed on a surface ofthe printed circuit board 111, and terminal electrodes 120 (FIG. 13)used for surface mounting are formed on a back side of the printedcircuit board 111. The wiring patterns 113 are connected to the terminalelectrodes 120 by respective electrodes 118 formed on an innercircumferential surface of respective through holes 112. The terminalelectrodes 120, the wiring patterns 113, and the electrodes 118 on theinner circumferential surface of the through holes 112 are typicallyformed by plating gold on copper. The through holes 112 are filled withsolder 119.

[0006] As indicated in FIG. 10, a semiconductor element 114 isdie-attached to the printed circuit board ill using epoxy resin orsilver paste, and the semiconductor element 114 and the wiring pattern113 are bonded to each other by a wire 115 of gold or the like. Then, adam 116 (FIG. 11) is provided on a circumferential edge part of theprinted circuit board 111 and a thermosetting epoxy resin 117 is appliedto the surface of the printed circuit board 111 on which thesemiconductor element 114 is mounted. Because the through holes 112 arefilled with solder 119, the applied resin 117 does not enter the throughholes 112. The resin 117 is then hardened through heating, cooling at aroom temperature, irradiation of ultraviolet ray, or the like.

[0007] The printed circuit board is cut and split along lines passingapproximately through center points of the through holes 112 by a dicingblade, and the electrode on the inner circumferential surface of thethrough holes 112 (as indicated in FIGS. 12, and 13) becomes a sideelectrode 118. In this way, a plurality of electronic parts, eachincluding one or more electronic components which are mounted on acircuit board having a terminal electrode 120 on the back side thereof,are obtained.

[0008] In conventional electronic parts and in the conventional methodfor manufacturing those parts, the sealing resin is fully hardenedbefore the mother board is split into smaller pieces. As a result, theresin is very hard when the electronic part is cut by the dicing blade.The inventors have discovered that this causes various problems.Specifically, if the dicing is carried out when the resin has been fullyhardened, micro-cracks 122 (FIG. 14) can be formed in the resin by theimpact of the dicing blade. When micro-cracks 122 are formed, largercracks are caused as a result of water being absorbed in themicro-cracks 122 and the reliability of the electronic parts isdegraded.

[0009] Also, in the conventional process after the sealing resin hashardened to its final degree of hardness, the filler and other elementsadded to the resin for the purpose of changing the coefficient of linearexpansion of the resin is exposed in the cut section of the resin. Inthe condition where the filler, etc., is exposed in the cut section ofthe resin, the resin surface is in a rough condition having a largenumber of pores, and there is a problem that water is absorbed from thepores and the reliability of the electronic part is degraded.

[0010] In addition, the coefficient of linear expansion of the motherboard is different from that of the sealing resin, and the resin shrinkswhen hardened. As a result, the mother board is warped when the resin ishardened as indicated in a simplified side view in FIG. 15. In thedicing process, it is necessary that the mother board and the resin beflat to achieve the correct dicing. Because the mother board is warped,the effectiveness of the dicing is suppressed.

SUMMARY OF THE INVENTION

[0011] The manufacturing method of the present invention comprises thesteps of: semi-curing a thermosetting resin located on the surface of amother board on which one or more electronic components are located to astage 2 condition, at least some of the electronic components beingencapsulated in the thermosetting resin; splitting the mother board intoindividual circuit boards, at least a plurality of the circuit boardshaving at least one electronic component encapsulated in the resin andmounted on the circuit board so as to form a plurality of electronicparts; and heating at least some of the individual electronic parts sothat the thermosetting resin is first melted and is then permanentlycured.

[0012] Since the mother board is split into individual electronic partswhile the resin is in the stage B condition, the mother board is notwarped when the splitting takes place.

[0013] Further, since the mother board is split into individualelectronic parts while the resin is in the stage 2 condition and theresin is subsequently permanently hardened to a final condition afterthe mother board is split into individual electronic parts, micro-cracksgenerated in splitting the mother board are removed when the resin isremelted-in the process of permanently hardening the resin.

[0014] The heating step used to finally harden the resin may be socontrolled that the thermosetting resin on the divided mother boardmelts to cover a portion of a side surface of the divided mother board.In the case, the resin surface is covered with a dense resin film, andthe resistance against separation of the resin and the resistanceagainst humidity are improved.

[0015] The manufacturing method of electronic parts may furthercomprises the step of providing a sheet on a surface of said resinbefore the semi-curing step. As a result, the surface of the resin canbe made flat by the force such as the surface tension. This step isparticularly useful when a suction device is used to mount theelectronic parts.

[0016] The thermosetting resin providing on the surface of the motherboard may be a pellet shape making the use of a dam unnecessary.

[0017] The electronic components may be arranged on the mother board ina matrix to facilitate the splitting process.

[0018] The manufacturing method may further comprises the step ofarranging the individual electronic parts with intervals therebetweenafter the splitting step. This ensures that adjacent electronic partswill not be adhered to each other through re-melting of the resin.

[0019] An electronic parts according to the present invention comprises:a circuit board; at least one electronic component mounted on thecircuit board; and a thermosetting resin provided on the surface of thecircuit board so as to seal the at least one electronic component, thethermosetting resin having a top surface layer which has a densitygreater than the inside thereof. The thermosetting layer may cover aportion of a side surface of the circuit board.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] For the purpose of illustrating the invention, there is shown inthe drawings several forms which are presently preferred, it beingunderstood, however, that the invention is not limited to the precisearrangements and instrumentalities shown.

[0021]FIG. 1 is a perspective view illustrating one process of amanufacturing method of an electronic part in accordance with a firstembodiment of the present invention.

[0022]FIG. 2 is a perspective view illustrating one process of amanufacturing method of an electronic part in accordance with the firstembodiment of the present invention.

[0023]FIG. 3 is a perspective view illustrating one process of amanufacturing method of an electronic part in accordance with the firstembodiment of the present invention.

[0024]FIG. 4 is a perspective view illustrating an electronic part to beobtained by the manufacturing method of the present invention.

[0025]FIG. 5 is a sectional view taken along the line 5-5 of FIG. 4.

[0026]FIG. 6 is a perspective view illustrating another electronic partsto be obtained by the manufacturing method of the present invention.

[0027]FIG. 7 is a perspective view illustrating one process of amanufacturing method of an electronic part according to a secondembodiment of the present invention.

[0028]FIG. 8 is a sectional view illustrating one process of amanufacturing method of an electronic part according to the secondembodiment of the present invention.

[0029]FIG. 9 is a perspective view illustrating one process of amanufacturing method of a conventional electronic part.

[0030]FIG. 10 is a perspective view illustrating one process of amanufacturing method of a conventional electronic part.

[0031]FIG. 11 is a perspective view illustrating one process of amanufacturing method of a conventional electronic part.

[0032]FIG. 12 is a perspective view illustrating an electronic part tobe obtained by a manufacturing method of a conventional electronic part.

[0033]FIG. 13 is a sectional view taken along the line 13-13 of FIG. 12.

[0034]FIG. 14 is a sectional view illustrating an electronic part inwhich micro-cracks are generated to be obtained by a manufacturingmethod of a conventional electronic part.

[0035]FIG. 15 is a simplified side view illustrating the warp of asubstrate.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0036] Hereinafter, the preferred embodiments of the present inventionare explained in detail with reference to the drawings wherein likenumerals indicate like elements.

[0037] In practice, a large number of element components are mounted ona single mother board, which is then divided into a large number ofsmaller pieces, each including at least one electronic component. Tosimplify the description of the invention, the figures shown includeonly four electronic components mounted on the mother board. Inpractice, however, a greater number of electronic components arenormally provided.

[0038] First, a printed circuit board 11 having through holes 12 locatedat the prescribed positions as indicated in FIG. 1, is prepared. Awiring pattern 13 is formed on the surface of the printed circuit board11, and terminal electrodes 20 (FIG.6) which are used for surfacemounting are formed on a back side of the printed circuit board 11. Eachwiring pattern 13 is connected to an associated terminal electrode-20preferably through an associated electrode 18 formed on an innercircumferential surface 16 of a respective through hole 12. Theelectrode 18 on the inner circumferential surface of the through holes12, the wiring pattern 13, and the terminal electrode 20 are preferablygold-plated on a copper material. In addition, the through holes 12 arefilled with soldier 19. The printed circuit board 11 may consist ofglass epoxy or other suitable materials such as aluminum andmulti-layered dielectric material.

[0039] As shown in FIG. 2, plurality of electronic components, such assemiconductor elements 14, are preferably die-attached to the printedcircuit board 11 by any suitable material such as epoxy resin or silverpaste. The semiconductors element 14 are bonded to the wiring patterns13 using gold wires or the like. While the electronic components of thedescribed embodiment are preferably semiconductor elements 14, otherelectronic components such as a capacitative element or an inductanceelement may be used.

[0040] A dam 16 is provided on a peripheral edge of the printed circuitboard 11 as indicated in FIG. 3, and a thermosetting resin 17, such asepoxy resin, is applied to the surface of the printed circuit board 11so as to encapsulate both the exposed portion of the upper surface ofthe printed circuit board 11 and the semiconductor elements 14. Theresin 17 may be a matrix resin in which a filler is added. Because thethrough holes 12 are filled with soldier 19, the thermosetting resin 17does not enter the through holes 12. While soldier is preferably usedfor this purpose, other materials may be used. For example, a resinwhich is soluble in alkaline aqueous solution may be used in which casethe resin is solved with the alkaline aqueous solution in a subsequentprocess. Another suitable alternative is to fill the through holes 12with a gold paste which is excellent in solder wettability. Othersuitable alternatives are to adhere an insulating film to the openingsof the through holes 12, or covering the through holes 12 with a solderresist.

[0041] Various thermosetting resins progressively move through stage A,stage 3 and stage C curing conditions. In stage A, the thermosettingresin is in an initial state and is uncured. In the stage B. thethermosetting resin is cured to a sufficient degree that it is no longerfluid but begins to upon the application of upon the application offurther heat and is subsequently melted and cured again. Finally, instage C, the thermosetting resin is completely cured and the resinreaches its final level of hardness.

[0042] In accordance with the preferred embodiment of the presentinvention, after the thermosetting resin 17 is applied to the printedcircuit board, it is hardened through heating, etc., until it reachesthe stage B condition where it is semi-cured. As known to those skilledin the art, this can be achieved by controlling the temperature andlength of the curing process.

[0043] If the curing of the thermosetting resin 17 is stopped when theresin is in the stage B condition, no large shrinking force will beapplied to the resin when the resin 17 is permanently hardened in stageC. As a result, the printed circuit board 11 will not be warped. Aliquid thermosetting epoxy resin is preferably used as the sealing resin17, but other resins such as an epoxy pellet capable of being formed inthe required shape may also be used. If the pellet is formed in a shapeto meet the size of the printed circuit board 11, use of the dam 16 canbe dispensed with, and the number of members used in manufacturingprocess can be reduced.

[0044] After the resin is cured to the stage B condition, the printedcircuit board 11 is preferably cut by a dicing blade along lines passingthrough approximately the center points of various through holes 12 tobe split into smaller pieces, each containing one or more electronicparts. The splitting of the printed circuit board into smaller piecesmay be achieved by other methods such as by breaking the board. If thethermosetting resin 17 is cured to stage B, the resin 17 will melt bythe heat applied during the dicing process, and the dicing blade willnot be severely loaded.

[0045] After the dicing process has been completed, the thermosettingresin 17 in the individual electronic parts is further cured by heatinguntil the curing is completed and the resin reaches stage C. As theresin 17 melts, it will fill any micro-cracks which may have been formedduring the dicing operation. In addition, after the dicing operation,the cut sections of the resin 17 are in a condition where the addedfiller, etc. is exposed, and the cut section of the resin 17 is in arough condition where a large number of pores are present. However, thesurface of the resin 17 is covered with a dense resin film when theresin 17 is melted during the final curing process. Therefore, it isdifficult for water to be absorbed from the surface of the resin 17, andthe reliability of the electronic parts is improved.

[0046] The electrode on the inner circumferential surface of the throughholes 12 where the electronic part has been cut is best shown in FIG. 4and in FIG. 5. These electrodes become side electrodes 18, and anelectronic part having a terminal electrode 20 on its back side isobtained. By controlling the time period in which heat is applied to theresin 17 to permanently harden the resin (i.e., to bring it to stage C),it is possible to ensure that the resin sags over a portion of the sideelectrodes 18 as shown in FIG. 6. This has the desired effect ofstrengthening the connection between the resin 17 and the printedcircuit board 11 and eliminating the absorption of water from the edgeparts of the substrate. This improves the resistance of the electronicparts against the humidity.

[0047] A second embodiment of the electronic part and method formanufacturing the same in accordance with-the principles of the presentinvention are described with reference to FIGS. 7 and 8. The explanationis same as that of the first embodiment in general, the same symbols areattached to the same elements as those of the previous embodiment andonly the elements specific to the second embodiment are described.

[0048] In this embodiment, the sealing thermosetting epoxy resin 17 isapplied to the printed circuit board 11 on which the semiconductorelement 14 are mounted, and then, a sheet 21, consisting of the resin orthe like, is carefully applied to cover the surface of the sealing resin17 so that no bubbles are contained in a top surface of the appliedresin 17 as indicated in FIG. 7. Then, the sealing resin 17 is heated tothe stage B condition. In the electronic part to be obtained throughthis process, the surface of the sealing resin 17 becomes flat asindicated in the sectional view of FIG. 8 by the sheet 21 consisting ofthe resin. This embodiment is particularly useful when a suction deviceor the like is to be used in the mounting of the electronic component.While sheet 21 preferably consists of resin or the like, other materialssuch as a non-woven fabric consisting of glass fiber may be used. Also,a pellet of thermosetting epoxy resin on which a sheet of resin isapplied or with which a non-woven fabric is impregnated may be placed onthe mother board and heated to be hardened.

[0049] In the disclosed embodiments, the printed circuit board havethrough holes formed therein. However, the invention is not so limited.For example, the terminal structure to be used in the connection to theoutside may be of LGA type or BGA type. The present invention may beapplied to any system where the mother board is split into smallerpieces to obtain individual pieces electronic components.

[0050] While preferred embodiments of the invention have been disclosed,various modes of carrying out the principles disclosed herein arecontemplated as being within the scope of the following claims.Therefore, it is understood that the scope of the invention is not to belimited except as otherwise set forth in the claims.

What is claimed is:
 1. A method of manufacturing electronic parts, themethod comprising: semi-curing a thermosetting resin located on thesurface of a mother board on which one or more electronic components arelocated to a stage B condition, at least some of the electroniccomponents being encapsulated in the thermosetting resin; splitting themother board into individual circuit boards, at least a plurality of thecircuit boards having at least one electronic component encapsulated inthe resin and mounted on the circuit board so as to form a plurality ofelectronic parts; and heating at least some of the individual electronicparts so that the thermosetting resin is first melted and is thenpermanently cured.
 2. A method according to claim 1 , wherein each ofthe individual circuit boards has at least one electronic componentlocated thereon, the at least one electronic component beingencapsulated in the resin.
 3. A method according to claim 2 , whereinthe heating step is applied to each of the electronic parts.
 4. A methodaccording to claim 3 , wherein, for each of the electronic parts, theheating step is carried out at a temperature and over a time periodwhich causes the thermosetting resin to melt and cover at least aportion of a side surface of the circuit board.
 5. A method according toclaim 4 , wherein the heating step is applied to all of the electronicparts simultaneously.
 6. A method according to claim 3 , furtherincluding the step of providing a sheet on an exposed surface of theresin before the semi-curing step.
 7. A method according to claim 1 ,wherein the heating step is applied to each of the electronic parts. 8.A method according to claim 1 , further including the steps of: mountinga plurality of electronic components on the surface of the mother boardprior to the semi-curing step; and providing the thermosetting resin onthe surface of the mother board and encapsulating at least some of theelectronic components after the mounting step but before the semi-curingstep.
 9. A method according to claim 8 , further including the step ofpreparing the mother board prior to the mounting step.
 10. A methodaccording to claim 8 , wherein the thermosetting resin provided on thesurface of the mother board is a pellet shape.
 11. A method according toclaim 1 , wherein, for each of the electronic parts, the heating step iscarried out at a temperature and over a time period which causes thethermosetting resin to melt and cover at least a portion of a sidesurface of the circuit board.
 12. A method according to claim 11 ,wherein the heating step is applied to all of the electronic partssimultaneously.
 13. A method according to claim 1 , further includingthe step of providing a sheet on an exposed surface of the resin beforethe semi-curing step.
 14. A method according to claim 1 , wherein theelectronic components are arranged on the mother board in a matrix. 15.A method according to claim 1 ,. further comprising the step ofseparating the individual electronic parts with intervals therebetweenafter the splitting step and before the heating step.
 16. An electronicpart, comprising: a circuit board; at least one electronic componentmounted on a main surface of the circuit board; and a thermosettingresin located on the surface of the circuit board and encapsulating atleast one of the at least one electronic component, the thermosettingresin having a top surface layer which has a density greater then aninner layer thereof.
 17. An electronic part according to claim 14 ,wherein the thermosetting layer covers at least a side portion of thecircuit board.
 18. An electronic part according to claim 13 , whereinthe side surface is substantially perpendicular to the main surface ofthe circuit board.